1. Field of the Invention
The invention relates generally to a method for fabricating a microelectronic structure, such as a semiconductor structure. More particularly, the invention relates to a laser annealing method for fabricating microelectronic structures, such as semiconductor structures.
2. Description of the Related Art
Common when fabricating microelectronic structures, and in particular when fabricating semiconductor structures, is the use of thermal annealing methods. Thermal annealing methods are often used in conjunction with other microelectronic fabrication methods. For example, thermal annealing methods are often used subsequent to, and in conjunction with, ion implantation methods for purposes of repairing ion implantation induced damage within a semiconductor substrate. Alternatively, thermal annealing methods are also used for forming, or subsequently annealing, metal silicide layers that, in turn, provide low contact resistance contact regions within semiconductor devices and semiconductor structures.
Conventional thermal annealing methods such as, for example, rapid thermal annealing methods and batch furnace annealing methods, typically lack a precision of thermal exposure (i.e., a thermal budget) that is generally required when a plurality of semiconductor device types is integrated onto a single semiconductor substrate. Such conventional thermal annealing methods also typically lack a possibility of spatial discrimination and control that is often also desirable when thermally annealing a plurality of semiconductor device types that is integrated onto a single semiconductor substrate. Thus, in order to provide for enhanced thermal annealing precision and enhanced thermal annealing spatial control, optically induced thermal annealing methods (i.e., opto-thermal methods such as, laser annealing methods) are often used for thermally annealing semiconductor substrates.
Although laser annealing methods are often essential within semiconductor structure fabrication, laser annealing methods are nonetheless also not without problems. As semiconductor structure dimensions continue to decrease and semiconductor device fabrication and integration complexity continues to increase, additional thermal annealing precision and spatial discrimination advances are needed for opto-thermal annealing methods.
Various laser induced annealing methods having enhanced capabilities are known in the semiconductor fabrication art.
For example, Tsukamoto, in U.S. Pat. No. 5,401,666, teaches a laser annealing method for selectively thermally annealing a gate electrode with respect to a source/drain region within a metal oxide semiconductor field effect transistor (MOSFET) device. This prior art method uses a laser reflectance control layer formed upon both the gate electrode and the source/drain region. The prior art laser reflectance control layer has a dimension optimized for reflection at the gate electrode and a different dimension optimized for absorbance at the source/drain region.
In addition, Offord et al., in U.S. Statutory Invention Registration H1637, teaches a laser annealing method for assisting in fabrication of bipolar transistors within silicon-on-sapphire (SOS) substrates. This prior art method uses an aluminum mask intended to reflect laser radiation from silicon layer regions within the SOS substrate where melting is not desired.
Further, Essaian et al., in U.S. Pat. No. 6,355,544, teaches a selective laser annealing method for incorporating a comparatively high dopant concentration (i.e., 1e18 to 1e21 dopant atoms per cubic centimeter) into a semiconductor substrate. This particular prior art method uses: (1) a doped spin-on-glass (SOG) layer as a dopant source layer contacting the semiconductor substrate; in conjunction with (2) a patterned anti-reflective coating (ARC) layer that assists in melting and interdiffusing specific portions of the SOG layer and the semiconductor substrate.
Dimensions of semiconductor devices and semiconductor structures are certain to continue to decrease. As a result, a need for both thermal annealing precision and spatial discrimination will continue to exist when laser annealing semiconductor substrates.